Fluorine-containing compounds, and particularly perfluoro compounds in which all hydrogen atoms of a hydrocarbon compound have been replaced with fluorine, have unique properties such as chemical stability and water and oil repellency, and are expected to be used in various applications such as pharmaceuticals, agricultural chemicals, polymers, functional products, surfactants, cleaners and various other chemical products and synthetic intermediates thereof.
A typical known example of a process for producing perfluoro compounds is electrolytic fluorination. Electrolytic fluorination is a process in which a raw material compound and hydrogen fluoride are placed in an electrolytic cell and current is applied between electrodes to carry out a fluorination reaction that uses hydrogen fluoride for the fluorine source. However, electrolytic fluorination requires considerable equipment costs. In addition, the raw material compound is susceptible to the occurrence of cleavage of carbon-carbon bonds and isomerization during reaction of the raw material compound with hydrogen fluoride, thereby making it difficult to obtain a target compound at high purity and high yield.
In addition, other known examples of processes for producing fluorine-containing compounds include a process that uses fluorine gas in a vapor phase, and a process that uses a higher metal fluoride produced from a metal fluoride and fluorine gas. However, these conventional fluorination processes were associated with difficulties in controlling the reaction due to the violent reactivity of fluorine gas as well as difficulty in handling the fluorine gas.
“Liquid-phase fluorination” has been proposed as a modified process for fluorinating the raw material compounds. “Liquid-phase fluorination” uses a perfluorocarbon for the solvent, and continuously supplies fluorine gas and a raw material diluted with the solvent in a state in which the solvent is saturated with the fluorine gas by dissolving the fluorine gas therein (Patent Document 1). According to this process, fluorination can be carried out while inhibiting a decomposition reaction of the raw material. However, in order to use the solvent with fluorine dissolved therein, the solvent is limited to a perfluorocarbon that is stable in fluorine. Thus, those compounds able to be fluorinated with this process are limited to those that dissolve in perfluorocarbons. Consequently, it is difficult to apply this process to ordinary hydrocarbon compounds to the poor solubility thereof.
Therefore, a process has been proposed in which an ester compound that easily dissolves in perfluorocarbons is synthesized by a reaction between an alcohol and a perfluorocarbonyl compound (see formula (I) below), followed by carrying out fluorination in the liquid phase using the resulting ester compound for the raw material (see formula (II) below) (Patent Document 2). By thermally decomposing the perfluoro compound obtained in formula (II) below with a nucleophile, a perfluoroacyl compound can be obtained that is derived from the raw material alcohol (see formula (III) below).CnH2n+1CH2OH+CmF2m+1COF→CmF2m+1COOCH2CnH2n+1  (I)CmF2m+1COOCH2CnH2n+1→CmF2m+1COOCF2CnF2n+1  (II)CmF2m+1COOCF2CnF2n+1→CnF2n+1COF+CmF2m+1COF  (III)
According to this process, even in the case of a higher alcohol that does not dissolve in perfluorocarbon as is, a liquid-phase fluorination reaction can be applied since the higher alcohol can be solubilized by esterifying with perfluorocarboxylic acid fluoride. On the other hand, the raw material in this process is limited to an esterifiable alcohol. In addition, an expensive perfluorocarbonyl compound is required. Moreover, a step for synthesizing ester, a step for separating the fluorination product, as well as decomposition and separation steps are required.
A process has also been proposed for fluorinating a raw material that does not dissolve in a fluorination reaction solvent in a liquid phase and in the presence of a substrate (such as benzene) that rapidly accelerates fluorination reactions by itself (Patent Document 3). According to this process, a fluorination reaction can be provided that uses a hydrocarbon compound for the raw material as is without using an expensive perfluorocarbonyl compound. In addition, pre-treatment or post-treatment steps such as esterification, decomposition or the like are not required. However, expenses are incurred for the added fluorination reaction substrate. What is more, since excess fluorine is consumed for fluorination and by-products are generated attributable to consumption of the excess fluorine, a step is necessary for removing those by-products. In addition, raw material compounds to which this process can be applied are limited to compounds such as highly chlorinated compounds that hardly react at all with fluorine gas even if introduced undiluted into the reaction atmosphere.
[Patent Document 1] U.S. Pat. No. 5,093,432
[Patent Document 2] WO 00/56694
[Patent Document 3] Japanese Unexamined Patent Application, First Publication No. 2006-131620